1. Field Of The invention
This invention relates to a lubricating system for an injection molding machine, more particularly to a lubricating system which is efficient and relatively inexpensive.
2. Description Of The Related Art Referring to FIG. 1, a common injection molding machine includes an elongated main body (A) which is adapted to be provided with a motor (not shown), an oil tank (not shown), an oil system (not shown), and a control circuit system (not shown), etc. therein. A material feeding system (B) is mounted on one end portion of the main body (A), and a mold pressing system (C) is mounted on the other end portion of the main body (A) and accepts material from the material feeding system (B) for molding. Referring to FIG. 2, the mold pressing system (C) includes a stationary mold half unit (C1), a stationary wall (C2), four horizontal longer connecting rods (C3), a movable mold half unit (C4), two connecting plates (C5), a toggle mechanism (C6), a mold pressing hydraulic cylinder (C7), a connecting cross member (C8) and two shorter connecting rods (C9). The stationary mold half unit (C1) and the stationary wall (C2) are adapted to be fixed on the main body (A) of the molding machine and are spaced apart and are aligned with each other. Each of the longer connecting rods (C3) is connected securely and perpendicularly to one corner of the stationary mold half unit (C1) at one end and is connected securely to one corner of the stationary wall (C2) at the other end. The movable mold half unit (C4) is mounted movably on the connecting rods (C3) so as to be moved toward and away from the stationary mold half unit (C1) along the connecting rods (C3). The two connecting plates (C5) are disposed between the stationary wall (C2) and the movable mold half unit (C4). One of the connecting plates (C5) interconnects the upper two connecting rods (C3), while the other one of the connecting plates (C5) interconnects the lower two connecting rods (C3). The toggle mechanism (C6) is coupled with the stationary wall (C2) and the movable mold half unit (C4). The mold pressing hydraulic cylinder (C7) has a horizontal cylinder body which is connected to the stationary wall (C2) in such a manner that the outer end of the piston rod (C71) of the hydraulic cylinder (C7) can be activated hydraulically so as to move between the stationary wall (C2) and the connecting members (C5). One of the shorter connecting rods (C9) is disposed between the upper two connecting rods (C3) and interconnects the stationary wall (C2) and the upper one of the connecting plates (C5). The other one of the shorter connecting rods (C9) is disposed between the lower two connecting rods (C3) and interconnects the stationary wall (C2) and the lower one of the connecting plates (C5). The cross member (C8) is mounted movably on the connecting rods (C9) at the two vertical distal ends thereof and is coupled with the outer end of the piston rod (C71) at the center and with the toggle mechanism (C6) at the two horizontal distal ends thereof so as to be driven to activate the toggle mechanism (C6) in order to move the movable mold half unit (C4). Referring to FIG. 3, another type of mold pressing system (D) includes a stationary mold half unit (D1); a stationary wall (D2) which is aligned with the stationary mold half unit (D1) and which is spaced apart from the same; a number of connecting rods (D3), each of which is coupled with the stationary mold half unit (D1) at one end and with the stationary wall (D2) at the other end; a movable mold half unit (D4) mounted movably on the connecting rods (D3) so as to be moved toward and away from the stationary mold half unit (D1) along the connecting rods (D3); a toggle mechanism (D5) coupled with the movable mold half unit (D4) and the stationary wall (D2); and a mold pressing hydraulic cylinder (D6) having a cylinder body connected securely to the stationary wall (D2) and a piston rod coupled with the toggle mechanism (D5) in such a manner that the piston rod of the mold pressing hydraulic cylinder (D6) can be activated hydraulically to drive the toggle mechanism (D5) so as to move the movable mold half unit (D4).
Each of the toggle mechanisms (C6,D5) includes a plurality of members which are connected pivotally to each other by means of pivots (5,5'). When the piston rods (C71,D61) of the mold pressing hydraulic cylinders (C7,D6) are activated to drive the toggle mechanisms (C6,D5) so as to move the movable mold half unit (C4,D4) to press against the stationary mold half unit (C1,D1), the contact areas between the pivots (5,5') and the members suffer from a great action force, such as shearing and frictional force, due to the great pressure between the movable mold half unit (C4,D4) and the stationary mold half unit (C1,D1), thereby easily wearing the pivots (5,5'). If the pivots (5,5') are worn, the normal operation of the mold pressing system (C,D) will be affected. Furthermore, an inferior product will be produced. Therefore, most of the injection molding machines have a lubricating system provided thereon for lubricating the contact areas between the members and the pivots (5,5') of the toggle mechanism (C6,D5).
One kind of a lubricating system for lubricating the contact areas between the members and the pivots of the toggle mechanism includes a drip cup which has lubricating oil stored therein. The drip cup and the contact areas are joined together by oil passages so that the lubricating oil can drip naturally from the drip cup to the contact areas where lubrication is needed. The drawback of this lubricating system is that part of the contact areas, wherein the pivots and the members are in tight contact and/ or the contact areas are far away from the outlet of the oil passage, have no lubricating oil presented for lubrication due to the absence of a pressure which can force the lubricating oil to flow to these contact areas.
Another kind of a lubricating system includes a motor pump which can pump the lubricating oil to the contact areas through the oil passages, and an electric control box which is connected electrically to the motor pump so as to control the motor pump to force a predetermined amount of oil to those contact areas at a predetermined time interval (e.g. 100 c.c. of lubricating oil every 30 minutes). The drawback of this lubricating system is that it is very expensive. Furthermore, the pressure which is generated by the motor pump is insufficient to force a high-viscosity lubricating oil because of insufficient power. A large expense is necessary in order to acquire an adequate and powerful motor pump. Thus, the aforementioned problems in the preceding lubricating system cannot be overcome by this lubricating system due to the relatively low viscosity of the lubricating oil which was used and to the insufficient power of the motor pump. Because of the low viscosity of the lubricating oil, the lubricating oil cannot flow into the tight contact areas even if the oil feeding time interval is minimized and/ or the amount of lubricating oil in one pumping action is increased. Furthermore, the excessive lubricating oil is wasted and can cause contamination problems.